Refractive errors of the eye such as myopia, hyperopia, and astigmatism are among the most commonly experienced eye problems. The corrective measures for these problems have been either glasses or contact lenses. In recent years, however, numerous attempts at surgical correction of refractive errors have been attempted.
One such technique is radial keratotomy, in which a surgeon makes 8-16 slices in the cornea that radiate outwardly from the pupil like spokes of a wheel. These cuts weaken the cornea so its edges bulge and the center flattens to refocus the light. The surgery takes about 15 minutes, can be done in a surgeon's office, and requires only a few days for the eye to recover. While this surgical technique is relatively safe in the short term, there are many drawbacks such as undercorrected vision, overcorrected vision, development of astigmatisms, glare from the surgical scars, and continued changing vision. Also, radial keratotomy is not reversible.
A second technique is to freeze a piece of cadaver cornea and grind it on a lathe to a predetermined corrective power. Once the tissue has been shaped, it is thawed and sewn onto the eye. If the newly-sewn cornea fails to correct the problem, the surgeon removes it and replaces it with another one.
However, there are problems with this technique. Grinding the frozen corneas into a contact lens is extremely difficult, and at the moment, there is only one institution which has the facilities to do it.
A third surgical approach, called keratophakia, sandwiches a thin layer of soft, pliable, transparent plastic into the middle of the cornea like icing between two halves of a cookie. The inserted material changes the shape of the cornea to refocus the light and correct vision.
The implanted material, called a hydrogel, consists of the same chemicals found in extended-wear contact lenses. And like contacts, hydrogels should give predictable correction because they can be precisely ground on a machine.
Keratophakia is also not without technical drawbacks. Not only is splitting the cornea in half a difficult procedure, after this, the surgeon must evenly insert the hydrogel, and then sew down the flap of the cornea. Since the tolerances are to fractions of a millimeter of curvature, it is easy to be off.
A fourth approach has been reported wherein a continuous plastic lens is placed on top of a recipient's cornea and held in place by donor corneal tissue. This approach, however has been unsuccessful because the donor cornea becomes necrotic, i.e., dies, due to a lack of a supply of nutrients from the recipient's eye.
Thus, there is a continuing need for a safe, reversible, and simple surgical treatment for refractive errors of the eye.